Help me explain my gap in working?

Hi I will try to keep this brief. Basically I was working in my dads company as an office manager, I left there and started working in a retail position. During this time I was studying. I injured my ankle and left the retail position to focus on studying (also I hated retail).

While being unemployed for 6/7 months I completed two courses Which made me qualified to teach/assess in further education (which is what I really want to do). After having an interview I was advise to volunteer in a college to get some work experience which I'm happy to do.

In the meantime I desperately need to earn some money, so I have been applying for admin jobs.

Now I'm wondering when they say why did you stop working as an office manager (I have left that as my last position) what do I say?

The truth is I have been studying to get into teaching, but I feel like the employers won't want to employ someone who intends on leaving soon to pursue a different career.

I have been speaking to a company that needs a pa, it's only 13 hours per week and good money per hour so I want to get this job as will give me plenty of spare time for volunteering.

I would say just be honest. IME employers are generally quite realistic about how attractive their jobs are and how long people can be expected to stay and they would probably not be expecting undying long term commitment to a role like the one you describe.